They don't work quite the same way as svn externals, though, in a way that didn't work for us. In particular, they leave no good way to deal with merging in ups

They don't work quite the same way as svn externals, though, in a way that didn't work for us. In particular, they leave no good way to deal with merging in upstream changes in a submodule's code if you've also made some of your own (provisional) edits.